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VRF Billing

This guide explains how to estimate VRF 2.5 costs for both the subscription and direct funding methods.

Understanding transaction costs

For Chainlink VRF v2.5 to fulfill your requests, you must maintain enough funds in your subscription balance. Gas cost calculation includes the following variables:

  • Gas price: The current gas price, which fluctuates depending on network conditions.

  • Callback gas: The amount of gas used for the callback request that returns your requested random values.

  • Verification gas: The amount of gas used to verify randomness onchain.

The gas price depends on current network conditions. The callback gas depends on your callback function, and the number of random values in your request. The cost of each request is final only after the transaction is complete, but you define the limits you are willing to spend for the request with the following variables:

  • Gas lane: The maximum gas price you are willing to pay for a request in wei. Define this limit by specifying the appropriate keyHash in your request. The limits of each gas lane are important for handling gas price spikes when Chainlink VRF bumps the gas price to fulfill your request quickly.

  • Callback gas limit: Specifies the maximum amount of gas you are willing to spend on the callback request. Define this limit by specifying the callbackGasLimit value in your request.

Estimate gas costs

You need to pre-fund your subscription enough to meet the minimum subscription balance in order to have a buffer against gas volatility.

After the request is complete, the final gas cost is recorded based on how much gas is used for the verification and callback. The actual cost of the request is deducted from your subscription balance.

The total gas cost in wei for your request uses the following formula:

(Gas price * (Verification gas + Callback gas)) = total gas cost

If you're paying for VRF in LINK, the total gas cost is converted to LINK using the ETH/LINK data feed. In the unlikely event that the data feed is unavailable, the VRF coordinator uses the fallbackWeiPerUnitLink value for the conversion instead. The fallbackWeiPerUnitLink value is defined in the coordinator contract for your selected network.

Apply premium

The premium is charged as a percentage of the overall gas cost. The premium is defined in the coordinator contract. Premium percentages are listed there as whole integers. For example, a 20% premium is listed as 20.

(total gas cost) * ((100 + Premium percentage) / 100) = total request cost

The total request cost is charged to your subscription balance. Since you have the option to pay for VRF requests either in LINK or the native token for the network you're using, your subscription can have both a LINK balance and a native token balance. The premium is higher when you pay with native tokens than when you pay with LINK. For example, the premium percentage for using Ethereum is 24 if you pay with Ethereum, and 20 if you pay with LINK.

Subscription cost examples

These are example calculations of a VRF subscription request on Ethereum, shown in both ETH and LINK. The values for other supported networks are available on the Supported Networks page. The examples show how to estimate the following:

  • The minimum subscription balance, which is a higher amount you need to reserve before your request is processed. This provides a buffer in case gas prices go higher when processing the request. The VRF Subscription Manager displays your minimum subscription balance as Max Cost.
  • The actual cost of the request after it is processed, which is lower than the minimum subscription balance.

Estimate minimum subscription balance

These example calculations show an estimated minimum subscription balance for using VRF on Ethereum, shown in both ETH and LINK. The premium is higher when you pay with native tokens than when you pay with LINK.

ParameterValue
Gas lane500 gwei
Callback gas limit100000
Max verification gas200000
Premium percentage20
  1. Calculate the total gas cost, using the maximum possible gas price for the selected gas lane, the estimated maximum verification gas, and the full callback gas limit:

    Gas cost calculationTotal gas cost
    Gas price x (Verification gas + Callback gas)
    500 gwei x (200000 + 100000)150000000 gwei (0.15 ETH)
  2. Apply the premium percentage to get the total maximum cost of a request:

    Applying premium percentageMaximum request cost (ETH)
    Total gas cost (ETH) * ((100 + premium percentage)/100)
    0.15 ETH * ((100 + 20)/100)0.18 ETH
  3. Convert the total cost to LINK using the LINK/ETH feed. For this example, assume the feed returns a conversion value of Ξ0.005 ETH per 1 LINK.

    ETH to LINK cost conversionMaximum request cost (LINK)
    0.18 ETH / 0.005 ETH/LINK36 LINK

For this example request to go through, you need to reserve a minimum subscription balance of 36 LINK, but that does not mean the actual request will cost 36 LINK. Check the Max Cost in the Subscription Manager to view the minimum subscription balance for all your contracts. When your request is processed, the actual cost of the request is calculated and deducted from your subscription balance. See the next section for an example of how to calculate the actual request cost.

Estimate VRF request cost

These example calculations show a cost breakdown of a VRF subscription request on the Ethereum network. Check Etherscan for current gas prices.

ParameterValue
Actual gas price50 gwei
Callback gas used95000
Verification gas used115000
Premium percentage20
  1. Calculate the total gas cost:

    Gas cost calculationTotal gas cost
    Gas price x (Verification gas + Callback gas)
    50 gwei x (115000 + 95000)10500000 gwei (0.0105 ETH)
  2. Apply the premium percentage to get the total cost of a request:

    Applying premium percentageTotal request cost (ETH)
    Total gas cost (ETH) * ((100 + premium percentage)/100)
    0.0105 ETH * ((100 + 20)/100)0.0126 ETH
  3. Convert the total cost to LINK using the LINK/ETH feed. For this example, assume the feed returns a conversion value of Ξ0.005 ETH per 1 LINK.

    ETH to LINK cost conversionTotal gas cost (LINK)
    0.0126 ETH / 0.005 ETH/LINK2.52 LINK

This example request would cost 2.52 LINK, which is deducted from your subscription balance.

Direct funding cost examples

These are example calculations of a VRF direct funding request on Ethereum, shown in both ETH and LINK. The values for other supported networks are available on the Supported Networks page.

ParameterValue
Gas price50 gwei
Callback gas limit100000
Coordinator gas overhead (LINK)112000
Wrapper gas overhead13400
Coordinator gas overhead per word435
Number of random values (words)2
Wrapper premium percentage20
  1. Calculate the total gas cost:

    Gas cost calculationTotal gas cost
    Gas price _ (Coordinator overhead gas + Callback gas limit + Wrapper gas overhead + (Coordinator overhead gas per word _ Number of words))
    50 gwei x (112000 + 100000 + 13400 + (435 * 2))11313500 gwei (0.0113135 ETH)
  2. Convert the gas cost to LINK using the LINK/ETH feed. For this example, assume the feed returns a conversion value of Ξ0.004 ETH per 1 LINK.

    ETH to LINK cost conversionTotal gas cost (LINK)
    0.0113135 ETH / 0.004 ETH/LINK2.828375 LINK
  3. Apply the premium percentage to get the total cost of a request:

    Applying premium percentageRequest cost (LINK)
    Total gas cost (LINK) * ((100 + premium percentage)/100)
    (2.828375 LINK * (100 + 20))/100)3.39405 LINK

This example request would cost 3.39405 LINK.

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